With modern scanning technologies, scientists can see which parts of the brain become active when we undertake different activities. In the case of religion, it is therefore possible to see which parts of the brain are involved in prayer or meditation - but knowing this and understanding why we believe are two different things. In this remarkable book, neuroscientist Michael Trimble examines a broad range of neurological capabilities including art, poetry, music and language in order to trace the evolutionary development of belief and provide an explanation for this distinctly human capability.

Trimble states that his thoughts on this subject were inspired by his patients, many of whom suffer from epilepsy. He noted that while many great literary writers seem to have suffered from epilepsy (e.g. Dostoevsky), very few poets do, suggesting that the conditions of epilepsy suppress poetic ability but not literary talent. On the other hand, conditions such as manic-depression and cyclothymia appear to be relatively common in poets.

These observations led Trimble to consider which areas of the brain are involved in these processes and to then link this to the condition seen in some patients with brain damage known as "hyperreligiosity" - a state psychiatrists describe as being religious addiction.

To arrive at its conclusions, the book considers a number of human capabilities and mental states before looking at the evolutionary processes that may have created them and which may also have led to the development of our belief systems.

Of particular interest is the consideration of the right cerebral hemisphere and its relation to language, a topic Trimble feels has been neglected in the past. While Broca's and Wernicke's areas (the main regions associated with speech and language) are typically located in the left hemisphere, other critical aspects of language including our abilities to work with metaphor, prosody, and tone probably derive from the right hemisphere's special capabilities. In this way, Trimble draws a distinction between the in the less specific, softer and ethereal aspects of language, the "voice of God", and the more perfunctory aspects of communication derived from the left hemisphere, the "voice of man".

The thought is that since the left hemisphere aspects of language are motivated by the specific, defined and logical requirements of communication, they can be regarded as "coming from within" i.e. being motivated by our own requirements. On the other hand, the aspects of language that come from the right hemisphere may appear to be "derived from without" - the inspiration for poetry being one such example.

In making these observations Trimble is not attempting to either prove or disprove the existence of God, simply to explore the boundaries between the disciplines of neurology and psychology using one of the most complex subjects possible.

The scope of the book is vast and it is certainly not a "light read". But for anyone interested in the subject of the book or even in the general area of the evolution of the brain, Trimble provides an insightful guide to an extremely complex subject.